John Bercow's warning against rowing back on Christopher Kelly's reforms of MPs' expenses was unusually stern. Photograph: PA Wire/PA

The Speaker, John Bercow, today warned it would be catastrophic for the reputation of parliament if any attempt was made to row back on the sweeping reforms of MPs' expenses proposed by Sir Christopher Kelly last month.

The unusually stern remarks will be taken as a warning to the new chairman of the independent parliamentary standards authority, Sir Ian Kennedy, not to meddle with the package presented. Kennedy had appeared to misread the public mood by saying he felt no obligation to implement the Kelly reforms, and would look again at the proposed ban on employment of spouses and the use of taxpayers money on mortgages on MPs' second homes.

Kennedy was reported at the weekend to be close to resigning in view of the highly personalised attacks upon him.

Bercow is also understood to be disappointed at the timidity of some of the reforms to parliament due to be unveiled by a parliamentary select committee, chaired by the Labour MP Tony Wright, which has been looking at how to strengthen the power of backbenchers

In a BBC interview, Bercow said he did not see his role as the shop stewards of MPs' interests, but instead as an ambassador for parliament. Discussing the Kelly reforms, he said he recognised there would be an element of rough justice, but added: "We have delayed too long and done too little to justify having any right to dictate the contours of the new system."

He continued: "I have candidly to say that denial, delay or dilution is simply not an option. Sir Christopher has produced his recommendations. In my view, they are very sensible, they should be embraced, I hope they will be implemented.

"The truth is that public trust in parliament has plummeted. The damage has been seismic. Public perception of the way in which we operate is so negative that it is necessary to accept a wholesale, fundamental and I think irrevocable change."

Bercow added that he hoped to see the reforms in place within weeks of the general election. In another word of warning to Kennedy, he said: "I don't think that we want a great, protracted debate or delay, I think it would be a catastrophic mistake to row back from that and to try to stick with a system that the public regards as excessively generous and fundamentally rotten to the core."

Wright's committee report is understood to recommend that only the chair of select committees are elected by secret ballot of MPs, leaving the appointment of most seats in the hands of party whips.

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